Conventionally, most fuel tanks used for storing fuel have been formed from a metal such as an aluminum alloy, and particularly in the case of integral tanks in the aircraft field, some or all of the members that constitute the tank are the same metal members that constitute the main wing, and have therefore been formed from a metal.
In recent years, in the field of transport machinery including aircraft, composite materials such as reinforced plastics have started to be used for structural elements such as the airframe or main wings in order to achieve weight reduction and associated improvements in performance.
In such cases, some or all of the integral tank, which is formed from the same components that constitute the main wing, is formed from a composite material. A variety of fuel tanks formed from composite materials have been proposed (for example, see Patent Literature 1 and 2).